Since designing and implementing a formal preventive maintenance (PM) program for variable frequency drives (VFDs) just under two years ago, Delta Automation has developed some interesting statistics related to the operational condition of VFDs. The generally accepted practice for most drive manufacturers is to advertise stats to their prospective customers regarding the extremely low failure rates of their equipment. This is usually in the fractional percentage range commonly on the order of less than 1%. The real question is what do these failure stats really mean in terms of a VFDs’ reliability?

Typically it means that for most manufacturer’s drives, if the installer follows the manufacturer‘s installation guidelines and the drive is properly sized, the failure upon start-up IS just that – extremely low. However, the more interesting question to ponder is what is the failure rate over the life of the drive – typically a span of 7-10 years under normal operating conditions and perhaps longer under ideal operating conditions. Note: ideal operating conditions include stable input power, a properly sized drive for the load, a low dust and/or low contaminant, dry environment and indeed proper PM.

After compiling data on hundreds of drives since Delta began the formal PM process, the PM stats breakdown like this:

The interesting “intangible” here is even drives that operate in pristine environments such as clean rooms or other non hostile areas are not immune to developing problems without having PM’s performed. Our experience has shown that these drives also tend to have a similar “repairs needed” profile as indicated above.

Please refer to the attached Drive lifecycle management graph courtesy of ABB Drives Services Division. This is an excellent pictorial representation of the impact of preventive maintenance on the useful life span of a VFD and its performance during that life span.

A lot depends upon the environment. By that I mean the ambient temperature variations and the quality of the incoming power. In a perfect environment, this VFD should have a lifespan of 7-10 years. With wildly varying temperatures or poor quality incoming power, the lifespan may be as short as just a few years.